1. Field of the Invention
The present invention relates in general to an impact absorber for a vehicle, and more particularly to an improvement in such an impact absorber having a small plate thickness.
2. Discussion of Prior Art
There is widely used an impact absorber for a vehicle, which has a tubular shape and which is to be disposed between a side member and a bumper beam of the vehicle, so as to be crushed like an accordion in its axial direction in the event of application of a compressive load to the impact absorber, for absorbing an impact energy (see Patent Documents 1 and 2). FIGS. 11A-11C are views for explaining one example of such an impact absorber, wherein FIG. 11A is a schematic plan view of a vicinity of a bumper beam 10 located on a front side of a vehicle body, as seen from an upper side of the vehicle body. As shown in FIG. 11A, crush boxes 14R, 14L as the impact absorbers are disposed on front end portions of right and left side members 12R, 12L, and the bumper beam 10 is attached at its right and left end portions to the side members 12R, 12L through the crush boxes 14R, 14L. FIG. 11B is a cross sectional view taken along line 11B-11B of FIG. 11A, i.e., a cross sectional view of vicinity of a right-side attached portion of the bumper beam 10. As shown in FIG. 11B, the crush box 14R has a tubular main body 20 having an octagonal shape or the like in its cross section, and a pair of attachment plates 22, 24 that are welded to be integrally fixed to axially opposite end portions of the main body 20. The crush box 14R is fixed at the attachment plates 22, 24 to the side member 12R and the bumper beam 10, for example, by bolts (not shown).
When receiving a compressive load F upon application of impact thereto in a direction from the vehicle front to the rear, the main body 20 is crushed like an accordion in the axial direction as shown in FIG. 11C, so that the deformation of the main body 20 absorbs the impact energy for thereby alleviating the impact applied to structural members of the vehicle such as the side member 12R. The crushing of the main body 20 like an accordion is a phenomenon that is caused by buckling in a large number of portions of the main body 20 (i.e., succession of small U-shaped bendings of the main body 20 as shown in FIG. 11C). Normally, the buckling is initiated in the bumper beam side, i.e., the impact application side, and then develops toward the vehicle-body side with elapse of time. The bumper beam 10 is symmetrical so that the left-side attached portion is constituted similarly as the right-side attached portion. This bumper beam 10 functions as a reinforcement (reinforcing member) of a bumper and also as an attachment member, and is integrally attached to a bumper body 16 formed of synthetic resin or the like.
FIGS. 12A-12D are sets of views for explaining some of arrangements for fixedly welding the main body 20 to one of the attachment plates 22, 24 (to the attachment plate 22 in the views). In the views of each set, an upper one of the views is a perspective view, while a lower one of views is a cross sectional view of a portion in which the main body 20 is fixedly welded to the attachment plate 22. FIG. 12A shows an arrangement in which a L-shaped bracket 30 is used to be fixed to the main body 20 and the attachment plate 22 by spot welding while the main body 20 is held in contact at its end portion with the attachment plate 22. FIG. 12B shows an arrangement in which the main body 20 is integrally fixed to the attachment plate 22 by arc welding while the main body 20 is held in contact at its end portion with the attachment plate 22. FIG. 12C shows an arrangement in which the main body 20 has a flange portion 32 provided by its end portion that is bent outwardly, and the main body 20 is integrally fixed to the attachment plate 22 at the flange portion 32 by spot welding. FIG. 12D shows an arrangement in which the attachment plate 22 has a flange portion 34 provided by its portion that is bent to protrude, and the main body 20 is integrally fixed to the flange portion 34 of the attachment plate 22 by spot welding.    [Patent Document 1] JP-H10-244955A    [Patent Document 2] JP-2002-104107A
However, in the arrangement shown in FIG. 12A, the bracket 30 has to be additionally prepared and welded, thereby increasing the number of the components and accordingly leading to the consequent increase in cost and weight. In the arrangement shown in FIG. 12C, the bent flange portion 32 induces the main body 20 to be easily bent or deformed upon application of load, thereby possibly deteriorating performance of absorbing the impact energy. In the arrangement shown in FIG. 12D, it is difficult to cause the main body 20 to be fixedly welded at its entire periphery to the attachment plate 22, thereby unlikely to be crushed evenly around the axis and possibly deteriorating performance of absorbing the impact energy.
On the other hand, in the arrangement shown in FIG. 12B in which the main body 20 is arc-welded to the attachment plate 22 while being held in contact at its end portion with the attachment plate 22, it is possible to obtain a stable performance of absorbing the impact energy. However, in this arrangement, the plate thickness requires to be, for example, at least 1.4 mm. This is because, if the plate thickness is too small, the main body 20 or the attachment plate 22 could be holed or its thickness could be made considerably small as a result of fusing by the welding, thereby easily causing deficiency such as reduction in the strength. It is thought that a suitable designing of configuration of the main body 20 could reduce the plate thickness while maintaining a predetermined degree of performance of absorbing the impact energy, and that the plate thickness of the main body 20 could be reduced where the purpose is directed to absorb the impact energy and reduce damage of the vehicle body upon application of a low load in the event of collision at a low speed such as 10 km/h or lower. However, there is a problem that the reduction of the plate thickness to be smaller than 1.4 mm is difficult when the main body 20 is intended to be fixed to the attachment plate 22 by arc welding while the main body 20 is held in contact with the attachment plate 22 as described above.
The present invention was made in the light of the background art discussed above. It is therefore an object of the invention to provide a light-weighted and inexpensive impact absorber having an arrangement which permits the main body to be satisfactorily fixed to the attachment plates by arc welding while being held in contact with the attachment plates even where the plate thickness of the main body is smaller than 1.4 mm, and which provides a satisfactory performance of absorbing the impact energy.